However, other military experts said Russian forces, in particular Putin’s “private army”, the Wagner Group mercenaries, had gained more ground in the town of Bakhmut which has seen some of the fiercest fighting of the war.
In its latest intelligence update, the Ministry of Defence in London said Russian generals had been prioritising in recent days an operation to try to encircle the Donetsk town of Avdiivka.
“However, Russian forces have made only marginal progress at the cost of heavy losses in armoured vehicles,” it said.
“Russia’s 10th Tank Regiment has likely lost a large proportion of its tanks while attempting to surround Avdiivka from the south.
“10th Tank Regiment’s losses have likely largely been due to tactically flawed frontal assaults similar to those in other recent failed Russian armoured attacks, such as around the town of Vuhledar.”
The briefing added: “The regiment is part of 3rd Army Corps, the first major new formation Russia stood up to support the invasion of Ukraine since August 2022.
“Numerous open-source accounts suggested that 3rd Army Corps has been particularly dogged by problems with ill-discipline and poor morale. Despite a likely period of training in Belarus, the formation still appears to display limited combat effectiveness.”
Avdiivka is 55 miles south of the largely destroyed mining town of Bakhmut where the Institute for the Study of War, a Washington-based think tank, said Russian forces had gain more territory in recent days.
Ukraine shut Avdiivka to civilians on Monday, with an official describing the town as a “post-apocalyptic” wasteland.
The Ukrainian military has warned that Avdiivka could become a “second Bakhmut”, which has been reduced to rubble in months of fighting described by both sides as a “meat grinder”. Russian forces say they are fighting street by street.
Ukrainian ground forces commander Colonel General Oleksandr Syrskyi, who said this month that a counterattack was not “far off”, visited frontline troops in the east and said his forces were still repelling attacks on Bakhmut.
Meanwhile, Ukrainian authorities said air defences shot down 12 drones near Kyiv on Monday and falling debris set a non-residential site ablaze. No casualties were reported.
Russia launched a total of 15 Iranian-made Shahed drones overnight on Ukraine, with Ukrainian forces destroying 14 of them, Ukraine’s military said early on Tuesday.
“The logic of the Russians’ actions is terror aimed at civilian infrastructure,” Ukrainian presidential chief of staff Andriy Yermak said on Telegram about the drone attacks.
“It won’t work, just like geopolitical blackmail.”
Since Putin’s invasion has stalled, he and other Russian officials have played up the prospect the war could escalate to involve nuclear weapons. On Saturday, he said he had struck a deal to station tactical nuclear weapons in Belarus.
Ukraine and its Western allies have slammed the plan.
Ukraine’s president Volodymyr Zelensky accused Russian troops of holding the Zaporizhzhia nuclear plant “hostage” and its safety could not be guaranteed until they left it.
Russian troops have occupied the nuclear power plant, Europe’s largest, since the early weeks of the invasion of Ukraine and have shown no inclination to relinquish control.
“Holding a nuclear power station hostage for more than a year - this is surely the worst thing that has ever happened in the history of European or world-wide nuclear power,” he said in his nightly video address.
He decried the Russian presence as “radiation blackmail”.
His comments followed a meeting with Rafael Grossi, the director general of the International Atomic Energy Agency (IAEA), at the Dnipro hydroelectric power station, northeast of the Zaporizhzhia plant.
Initiatives on restoring safety and security are “doomed to failure” without a withdrawal of Russian troops from the plant, Mr Zelensky said in comments posted on the presidential website.
Russia and Ukraine routinely accuse each other of shelling the Zaporizhzhia plant. Fighting around it and worries of a water shortage and that cooling systems could lose power have raised fears of a nuclear disaster.
A team of IAEA has since September been stationed at the plant, which Kyiv has accused Moscow of using as a shield for troops and military hardware.
Mr Grossi has repeatedly called for a safety zone around it and is due to visit it again this week. He has tried to negotiate with both sides but said in January that brokering a deal was getting harder.
Zaporizhzhia is one of four regions Russia claimed to annex in September after referendums criticised globally as shams. Russia views the plant as its territory, which Ukraine denies.
Mr Zelensky visited the southeastern Zaporizhzhia region on Monday, the latest stage of a tour of frontline regions since a top general said Ukraine’s counterattack could come soon.